A CCD photometric study of the late type contact binary EK Comae Berenices

We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 m telescope of IUCAA Girawali Observatory, India. The star was classified as a W UMa type binary of subtype-W by Samec et al. (1996). The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by Samec et al. (1996). A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature difference of ΔT = 141 ± 10 K between the components and an orbital inclination of i[°] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell effect is explained by the presence of a hot spot on the primary component.     

A photometric study of a weak-contact binary: V873 Per

We present a photometric study of a weak-contact binary V873 Per. New observations in BVR filter bands showed asymmetric light curves to be a negative type of the O’Connell effect, which can be described by magnetic activity of a cool spot on the more massive component. Our photometric solutions showed that V873 Per is a W-type with a mass ratio of q = 2.504(±0.0029), confirming the results of Samec et al. (2009). The derived contact degree was found to be f = 18.10%(±1.36%). Moreover, our analysis found the cyclic variation with the period of about 4 yr that could be due to existence of the third companion in the system or the mechanism of magnetic activity cycle in the binary. While available data indicated that the long-term orbital period tends to be stable rather than decreasing.     

A photometric study of the detached binary WY Hydrae with twin components

We present a multicolor photometry for the eclipsing binary WY Hydrae, observed on four nights of 2008 December. From our new observations and Carr’s data, the photometric solutions were deduced by using the updated W–D program. The results show that WY Hya is a detached binary with a mass ratio of q = 0.970(±0.005).By analyzing the O–C curve, it is found that there exists either a continuous period increase or a cyclic variation. From Eq. (2), the orbital period of WY Hya secularly increases at a rate of dP/dt = +3.56(±0.37) × 10^?7 days/yr, which may be interpreted by some mass transfer for the near-contact configuration or tidal dissipation. From Eq. (3), the period and semi-amplitude of the periodic oscillation are P₃ = 95.4(±4.2) yr and A = 0^d.0087(±0^d.0003), respectively. This may be likely attributed by light-time effect via the presence of the assumed third body. Assumed in the coplanar orbit with the binary, the mass of the third body should be M₃ = 0.18 M_⊙. If the unseen additional companion exists, it will extract angular momentum from the binary system. Finally, WY Hya with high fill-out factors (i.e., f_1,2 > 80%), may evolve into a semi-detached configuration.     

Absolute and geometric parameters of W UMa type contact binary TYC 1174-344-1

We present the results of our investigation on the geometrical and physical parameters of W UMa-type binary TYC1174-344-1 from analyzed CCD (BVRI) light curves and radial velocity data. The photometric data were obtained in 2009 at Ankara University Observatory (AUO) and the spectroscopic observations were made in 2008 at Astrophysical Observatory of Asiago (Italy). Light and radial velocity observations were analyzed simultaneously by using the well-known Wilson–Devinney (2007 revision) code to obtain absolute and geometrical parameters. According to our solutions, the system is found to be a low mass-ratio A-type W UMa system. Combining our photometric solution with the spectroscopic data, we derived mass and radii of the eclipsing system as M₁ = 1.381 M_⊙, M₂ = 0.258 M_⊙, R₁ = 1.449 R_⊙ and R₂ = 0.714 R_⊙. We finally discussed the evolutionary condition of the system.     

CCD Photometry of the W UMa type star QX Andromeda

We present new B- and V-band photometry of the W UMa-type binary system QX And, which is a member of the open cluster NGC 752. Revised orbital period and new ephemerides were given for the binary system based on the data of times of light minima. The result of a period analysis reveals that the system is undergoing a continuous orbital period increase during the past decades. The rate of period increasing turns out to be about 2.7 × 10^?7 d yr^?1. With the Wilson–Devinney code, a photometric solution is computed. It yields a contact configuration for the system with a filling factor of 0.361. Combining the results from the photometric solution along with that from the radial-velocity observations, we have determined the absolute parameters for the two components of the system. The masses, radii and luminosity of the primary and secondary stars are calculated as 1.43 ± 0.04 M_⊙, 1.45 ± 0.09 R_⊙, 2.87 ± 0.40 L_⊙ and 0.44 ± 0.02 M_⊙, 0.87 ± 0.05 R_⊙, 0.99 ± 0.13 L_⊙, respectively. The evolutionary status and physical nature of the contact binary system were discussed compared with the theoretical models.     

Orbital period investigations of two short-period early-type overcontact binaries BH Cen and V701 Sco in two extremely young galactic clusters IC 2944 and NGC 6383

Both V701 Sco and BH Cen are two early-type short-period overcontact systems (P = 0.^d762 and P = 0.^d792, respectively). V701 Sco is a member of the young galactic cluster NGC 6383, while BH Cen is a component of a younger galactic cluster IC 2944 where star formation is in process. They provide good opportunity to understand the formation and evolution of binary stars. In the present paper, orbital period changes of the two binaries are investigated. It is discovered that the orbital period of BH Cen shows a long-term increase with a rate of dP/dt = +1.70(±0.39) × 10⁻⁷ days/year while it undergoes a cyclic oscillation with a period of 44.6 years and an amplitude of A₃ = 0.^d0216. For V701 Sco, its O-C curve reveals a periodic change with a period of 41.2 years and amplitude of A₃ = 0.^d0158. The mass ratio of BH Cen is 0.84, but V701 Sco contains twin B1-1.5V type stars with a mass ratio of unit. The continuous period increase of BH Cen is caused by the mass transfer from the less massive component to the more massive one at a rate of dM₂/dt = 3.5 × 10⁻⁶ days/year.The cyclic period changes of both systems can be plausibly explained as the results of light-travel time effects suggesting that they are triple systems. The astrophysical parameters of the unseen tertiary components in the two systems have been determined. We think that the invisible tertiary components in both binaries played an important role in the formations and evolutions of the overcontact configurations by bringing angular momentum out from the central systems. For BH Cen, this process created the initial short period and will support its evolution into an overcontact configuration via a Case A mass transfer within the life time of the extremely young cluster IC 2944. For V701 Sco, two identical zero-age main-sequence components in an overcontact configuration suggest that it may have been formed by fission, possibly by the fission of the third body. The fact that no long-term continuous period variations were found for V701 Sco may suggest that an overcontact binary with the mass ratio of unity can be in an equilibrium revealing that the original configuration of the binary was overcontact as is its present state. It has been reported that faint stars in the two extremely young clusters are relatively scare. From the present study, it is shown that faint stars in young clusters are usually formed as companions of OB stars (including binaries). It is very difficult to detect them because of their low luminosity when compared with the more luminous OB stars.     

Absolute properties of the overcontact binary HH Boo

We obtained multi-colour light curves of the overcontact binary system HH Boo and analysed the orbital period variation of the system. Our analysis tentatively indicates either mass transfer from the secondary to the primary or mass loss from the system at a rate of -5.04 × 10⁻⁷ M_⊙ per year. Through a combined analysis of the published radial velocity curve and light curves, we determined an inclination (i) of 69°.71 ± 0°.16 and a semi-major axis (a) of 2.246 ± 0.064 R_⊙ for HH Boo. The masses of the primary and secondary components were found to be 0.92 ± 0.08 M_⊙ and 0.58 ± 0.06 M_⊙, respectively. The radius determined for the primary was 0.98 ± 0.03 R_⊙, while that determined for the secondary was 0.80 ± 0.02 R_⊙. We demonstrated that HH Boo is most likely a member of the A-type subclass of W UMa binaries.     

A photometric study of the W UMa-type binary DF Canum Venaticorum

We present new photometric observations for the eclipsing binary DF CVn, and determined five light minimum times. By using the Wilson–Devinney code, two sets of photometric solutions were deduced from our observations in 2009. The asymmetric light curves obtained on 2009 March 5 were modeled by a dark spot on the more massive component. The results indicate that DF CVn is a W-type weak-contact binary, with a mass ratio of q ～ 0.28 and an overcontact degree of f ～ 20%. From the O ? C curve of minimum times, it is found that there exists a cyclic variation, whose period and semi-amplitude are P₃ = 17.2(±0.9) year and A = 0.^d0070(±0.^d0008), respectively. This kind of cyclic oscillation may possibly result from the light-time effect due to the presence of an unseen third body. This kind of additional body may extract angular momentum from the central system. The low-amplitude changes of the light curves on a short-time scale (e.g., half a month) may be attributed to the dark spot activity, which may result in angular momentum loss via magnetic breaking. With angular momentum loss, the weak-contact binary DF CVn will evolve into a deep-contact configuration.     

A period investigation of two chromospherically active binary stars: RT Coronae Borealis and PW Herculis

Orbital period variations of two chromospherically active binary systems, RT CrB and PW Her, are presented. It is shown that the orbital period of RT CrB undergoes a cyclic oscillation with a period of 53.9 years. For PW Her, an alternate change, with a period of 42.7 years, is found to superimpose on a rapid secular increase (dP/dt=+3.53×10⁻⁶ days/year). If the period oscillations of those two systems are caused by the light-time effect of a third body, the analysis for RT CrB indicates that the third body would be a low-mass main-sequence star, while, for PW Her, the mass of the third body should be no less than 7.8 M_⊙. Since no spectral lines of the third body were seen in PW Her from the spectroscopic study by Popper [AJ 100 (1990) 247], if there is a third body in the system, it can only be a black hole. However, as both components in the two binary stars were showing strong chromospheric activity, the alternate period variations are more plausibly explained as the result of magnetic activity cycles. No secular period changes of RT CrB are found, which is in agreement with the detached evolved configuration of the system. The long-term period increase of PW Her may indicate that it is on an active phase of mass transfer (dm/dt=2.17×10⁻⁶ M_⊙/year).     

A γ Doradus candidate in eclipsing binary BD And?

The BVR photometric light curves of the eclipsing binary BD And were obtained in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the photometric solutions were derived. The results show that BD And is a detached binary system, whose components have a little temperature difference of about 40 K. By analyzing photometric available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.011 days and a period of 9.6 years. The results indicate that the periodic oscillation could be caused by a third component physically attached to the eclipsing binary. After removing the light variations due to the eclipses and proximity effects, the light-curve distortions are further explained by the pulsation of the primary component with a dominant period of ∼1 day. In accordance with the position of the primary component on the Hertzsprung–Russell diagram and its pulsation period, the primary component of BD And could be an excellent γ Doradus candidate. It is rarely phenomenon that a component of the eclipsing binary system is a γ Doradus variable.     

Cyclic period changes and the light-time effect in eclipsing binaries: A low-mass companion around the system VV Ursae Majoris

In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M_⊙, and the semi-major axis of its orbit is 10.75 AU.     

Photometric study of the newly discovered short period eclipsing binary 1SWASP J133105.91 + 121538.0

A total of 311 BVRI observations were carried out on 4 May 2013 for the new short period W UMa system 1SWASP J133105.91 + 121538.0 using the 1.88 m reflector telescope of Kottamia Astronomical Observatory (KAO) at NRIAG. A photometric solution of these light curves was obtained by means of Wilson–Devinney (WD) code. A spotted model was applied to treat the asymmetry of the light curve. The results show that the more massive component is hotter than the less massive one with about ΔT ∼ 300 K. The system is at a distance of 89 ± 3.6 pc. Based on the physical parameters of the system, we investigate the evolutionary state of the components. Both components are above the zero age main sequence (ZAMS) track by about 0.2 magnitudes.     

VRI photometry and light curve analysis of short period W UMa-Type 1SWASP J222514.69 + 361643.0

We present the first light curve analysis and modeling for the short period close binary 1SWASP J222514.69 + 361643.0. The results show that the system is in over contact with factor ƒ = 53%. The primary component is the massive and hotter one. The system is A-subtype W UMa eclipsing binary with spectral types K2 and K3, respectively.     

The detached eclipsing binary TX Her revisited

This paper presents new CCD Bessell BVRI light curves and photometric analysis of the Algol-type binary star TX Her. The CCD observations were carried out at Çanakkale Onsekiz Mart University Observatory in 2010. New BVRI light curves from this study and radial velocity curves from Popper (1970) were solved simultaneously using modern light and radial velocity curves synthesis methods. The general results show that TX Her is a well-detached eclipsing binary, however, both component stars fill at least half of their Roche lobes. A significant third light contribution to the total light of the system could not be determined. Using O–C residuals formed by the updated minima times, an orbital period study of the system was performed. It was confirmed that the tilted sinusoidal O–C variation corresponds to an apparent period variation caused by the light travel time effect due to an unseen third body. The following absolute parameters of the components were derived: M₁ = 1.62 ± 0.04 M_⊙, M₂ = 1.45 ± 0.03 M_⊙, R₁ = 1.69 ± 0.03 R_⊙, R₂ = 1.43 ± 0.03 R_⊙, L₁ = 8.21 ± 0.90 L_⊙ and L₂ = 3.64 ± 0.60 L_⊙. The distance to TX Her was calculated as 155 ± 10 pc, taking into account interstellar extinction. The position of the components of TX Her in the HR diagram are also discussed. The components are young stars with an age of ～500 Myr.     

The eclipsing binary star V380 Gem: First V and Rc light curve analysis and estimation of its absolute elements

We obtained complete V and R_c light curves of the eclipsing binary V380 Gem in 2012. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3366088 days. The 2003 version of the Wilson–Devinney code was used to analyze the light curves in the V and R_c bands simultaneously. It is shown that V380 Gem may be classified as an W-type W Ursae Majoris system with a high mass ratio q = 1.45, a degree of contact f = 10.6% the same temperature for both the components (ΔT = 10 K) and an orbital inclination of i  = 81.5°. Our observations show symmetric light curves in all passbands with brightness in both maxima at the same level. The absolute dimensions of V380 Gem are estimated and its dynamical evolution is inferred.     

Period studies of classical Algol-type binaries II: UX Leo,RW Mon,EQ Ori,XZ UMa and AX Vul

This study presents an investigation of the orbital period variations of five Algol type binaries, UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul based on all available minima times. The O–C diagrams of all systems exhibit a periodic variation superimposed on a downward parabolic segment. The mass loss due to magnetic braking effect in the cooler components is assumed to account for the parabolic variation with a downward shape, while it is suggested that the light-time effect (LITE) due to an unseen component around the eclipsing binaries explains the tilted sinusoidal changes in their O–C diagrams. The orbital period decrease rates for the systems are estimated as approximately between about 0.7 and 2.5 s per century. It is clearly seen that mass loss effect is more dominant than the expected mass transfer for classical Algols in this study. The minimum mass of the probable third bodies around the eclipsing pairs was calculated to be ?0.5 M_⊙ except for UX Leo, in which it was estimated to be approximately 0.9 M_⊙. In order to search for third lights in the light curves of five systems, the V-light curves of the systems were analyzed and their physical and photometric parameters were determined. For UX Leo, a significant third light contribution was determined. We found a very small third light that can be tested using multi-color light curves, for RW Mon, EQ Ori and XZ UMa, while a third light for AX Vul could not be exposed.     

Spectroscopic and photometric study of the contact binary BO CVn

We present the results of the study of the contact binary system BO CVn. We have obtained physical parameters of the components based on combined analysis of new, multi-color light curves and spectroscopic mass ratio. This is the first time the latter has been determined for this object. We derived the contact configuration for the system with a very high filling factor of about 88%. We were able to reproduce the observed light curve, namely the flat bottom of the secondary minimum, only if a third light has been added into the list of free parameters. The resulting third light contribution is significant, about 20–24%, while the absolute parameters of components are: M₁ = 1.16, M₂ = 0.39, R₁ = 1.62 and R₂ = 1.00 (in solar units).The O-C diagram shows an upward parabola which, under the conservative mass transfer assumption, would correspond to a mass transfer rate of dM/dt = 6.3 × 10^?8M_⊙/yr, matter being transferred from the less massive component to the more massive one. No cyclic, short-period variations have been found in the O-C diagram (but longer-term variations remain a possibility).     

Is V899 Herculis an unsolved quadruple system containing double close binary stars?

Orbital period variation of the W UMa-type eclipsing binary, V899 Herculis, discovered by the Hipparcos satellite was investigated based on all available photoelectric and CCD times of light minimum. It is discovered that the orbital period of the binary shows a cyclic change with an amplitude of 0.0117 days. The cyclic period change can be explained as the light-travel time orbit of a tertiary component in the system, which is in agreement with the spectroscopic result obtained by Lu et al. [Lu, W., Rucinski, S.M., Ogloza, W., 2001. AJ 122, 402] who found that the system, of which V899 Herculis is a fainter component (B), is a triple, even quadruple and with the photometric result obtained by Özdemir et al. [Özdemir, S., Demircan, O., Erdem, A., Cicek, C., Bulut, I., Soydugan, E., Soydugan, F., 2002. A&A 387, 240] who reported a large amount of third light (L₃ ∼ 0.68) of the system. The third body (A) rotates around the eclipsing pair in a period of 3.7 years. Lu et al. [Lu, W., Rucinski, S.M., Ogloza, W., 2001. AJ 122, 402] reported that the tertiary component is F5-type main-sequence star. However, the present analysis shows that the mass of the third component is no less than 2.8 M_⊙, which is larger than the mass of an F5-type main-sequence star suggesting that the tertiary component may be a non-eclipsing close binary. Therefore, the system may be a possible unsolved quadruple system containing double close binary stars. It is a good astrophysical laboratory to study the formation and evolution of binary and multiple system. The timescale for the formation of the G-type overcontact binary (V899 Herculis) via AML should be shorter than the main-sequence time of an F5-type star.     

Spectral and photometric behavior of SU UMa during quiescence and outburst states

We report the results of spectral and photometric observations of SU UMa. Available spectra from International Ultraviolet Explorer (IUE) and CCD photometry of five nights were used. Some profiles revealing the variations of some spectral lines at different times are presented. There is variation with time for photometric observations and the brightness of SU UMa is changed from 12.9 mag. to 15.6 mag in 5 nights with clear display of burst. The ultraviolet luminosity for emitting region is in the range of (6.9*10³⁰ erg s⁻¹). The mass accretion rate is in the range of (9.8*10⁻¹³ M_⊙yr⁻¹). The line flux modulations at different times can be explained in terms of the mass transfer instability model (Bath 1973).